Philip medaet



(No Model.)

. P. MEDART.

BELT PULLEY. No. 248,598. Patented Oct. 25,1881.v

ATTEST: INVENTOR:

Uwrrnn STATES PATENT Orrrce.

PHILIP MEDART, OF ST. LOUIS, MISSOURI, ASSIGNOR OF ONE-HALF TO WVILLIAM MEDART, OF SAME PLACE.

BELT-PU LLEY.

SPECIFICATION forming part of Letters Patent No. 248,598, dated October 25, 1881.

Application filed August 29, 1881.

To all whom it may concern:

Be it known that I, PHILIP MEDART, a citizen of the United States, and a resident of St. Louis, in the State. of Missouri, have invented certain new and useful Improvements in Belt- Pulleys, of which the following is a specification.

My improved pulley belongs to that class of pulleys composed of a separate spider, usually of cast metal, and awrought-metal rim, which is secured to the spider; and my invention consistsin a pulley which is perfectly true and accurately balanced-that is, a pulley in which the center of gravity and geometrical center or axiscoincide.

The belt-pulleys of various kinds in use prior to the date of my invention have all been more or less open to the objection of not being accurately balanced. This defect has been inherent in their structure. Thus, while cast pulleys are of accurate shape, they cannot be practically produced ofperfect balance,owing to theirregularityof the weight of the metal at different portions'of the rim, 'and'to contraction in cooling; and where pulleys of similar character to that herein shown have been made the spiders have not been properly prepared-that is, the spiders have not been operated upon so as to make the ends of their arms exactly concentric with the true center or axis of the pulley. The arms of the spider, owing to the impraclicability of makingperfectly accurate and smooth castings, and to contraction in cooling, will necessarily possess slight irregularities relatively to the center of the pulley, and unless these are removed and the ends of all the arms made exactly concentric with the pulley-axis the completed pulley will of necessity be imperfectly balanced. Substantially the same is true of composite pulleys of any characterthat is to say, the spider, however made, will be slightly imperfect in shape, and unless the irregularities are cured before applying the rim the completed pulley will notbe accurately balanced.

The advantages of having pulleys of abs0- lutely accurate balance and shape are numerous, and are so well known and sought after by those who use them that it is not deemed necessary to recite and explain them.

The accompanying drawing is a vertical section of a belt-pulley illustrating my invention.

(No model.)

In making my pulley, the cast-spider A is centered and bored. The ends of the arms or the faces of the bracket-lugs a, upon which the rim is laid, are then ground or turned off, by any suitablemachinery,exactlyconcentric with the axis of the pulley. By thus preparing the spider the rim B, which is rolled perfectly true and uniform in shape, will be exactly concentric at every point with the pulley-axis when laid around the spider, and the pulley will therefore be accurately balanced. In order to make the pulley even more truein shape and perfectly balanced, I then grind the rim concentrically with the axis.

The center of gravity of a pulley thus made is brought to coincide with its geometrical center more absolutely than has heretofore been done.

It will be obvious that if the pulley-arms are not firstground off concentrically with the axis, all of the inequalities incident to the operation of casting and cooling would remain as defects in the spider, and would be greatly aggravated by the grinding of the rim, because the lengths ofthe spider-armsbeing unequal without grinding when the pulley-rim is applied and ground, it will be cutaway nncquall vin some portions more and in others less-making it unequal in thickness, so that the final grinding operation, in order to make the pulley perfectly circular, will greatly increase its want of balance; but by preparing the spider as above described all defects are cured and pulleys of true shape and balance are produced.

I make no claim herein to the process of making the perfectly-balanced. pulley; but

What I claim is- 1. The improved belt pulley herein described, having the ends of the spiderarms ground off concentrically with the axis of the pulley.

2. The improved beltpulley herein described, in which the rim and the ends of the spider-arms are ground off concentrically with the axis of the pulley. I

In testimony whereof witness my hand, at St. Louis, Missouri, this 22d day of August, 1881.

PHILlP MEDART.

Witnesses:

WM. MEDART, R0131. BURNS. 

